1. Field of the Invention:
The present invention relates to an intermittent drive mechanism for use in an intermittently operative apparatus, such as an apparatus for intermittently feeding a tape-like flexible elongate material by and between a cooperative pair of feed and presser rollers.
2. Prior Art:
There are known various intermittent feed mechanisms of the type described. One such known mechanism is shown in FIG. 10, which mechanism comprises a gear ratchet including a drive pawl 101 pivoted to one end of a lever 102 and meshing with a toothed ratchet wheel 103 fixed on a drive shaft 104, the other end of the lever 102 being slidably fitted over an eccentric cam 105 connected with a driven shaft 106. Upon rotation of the drive shaft 104, the drive pawl 101 moves back and forth in the directions of the arrowheads A to thereby turn the ratchet wheel 103 and hence the driven shaft 106 stepwise in the counterclockwise direction. The drive mechanism further includes a friction brake unit composed of a brake drum 107 secured to the drive shaft 106, a pair of brake shoes 108, 109 secured to confronting inner edges of a pair of brake levers 110, 111 disposed on opposite sides of the brake drum 107, and a spring 112 acting between the brake shoes 108, 109 to urge them toward each other into frictional engagement with the brake drum 107.
The known intermittent drive mechanism thus constructed is disadvantageous in that it cannot precisely control the stepwise angular motion of the driven shaft 106 bacause the stopping timing of the stepwise motion is solely dependent on a friction or braking force exerted by the friction brake unit. The ratchet wheel 103 is likely to overrun while it is driven at a high speed. Furthermore, the contacting components, particularly the brake shoes 108, 109 and the drive pawl 101 are progressively worn out while in use, and hence a frequent adjustment or maintenance of such components is required. Another drawback is that the components in the drive mechanism themselves and other components driven by the drive mechanism are likely to be damaged due to undue shock forces applied thereto when the stepwise movement of the driven shaft 106 is started and stopped abruptly in such a manner that the angular speed of the drive shaft varies in a rectangular pulse-like fashion, as shown in FIG. 11.
Other prior art mechanisms are not satisfactory because they also have the foregoing drawbacks in greater or lesser degree.